What does a medicine have to prevent absorption of its contents before it reaches the small intestine?

A medicine must have a formulation that protects it from the acidic environment of the stomach and delays its release until it reaches the small intestine. This is often achieved through enteric coating, which is a polymer barrier that prevents dissolution in the stomach but allows the medicine to dissolve in the more neutral pH of the small intestine. Additionally, some medications might use controlled-release mechanisms to ensure gradual absorption.